Depends on which drive shafts you have. If you have an A1 or A2 configuration, you get to revel in the luxury of all the U-Joints being the same on the front and rear propeller shaft. If you have an original/A0, you'll need to look up your parts in the -24P vol 1 parts manual to be sure of correct fitment.
For those A1/A2 u-joints, you're dealing with a Dana/Spicer 1330-series axle, so you can buy off-the-shelf U-Joints with that information at any parts store. The OEM part AM General would have installed is a Federal Mogul 5-213X. You can buy them reasonably priced from Erik's (see link:
http://eriksmilitarysurplus.com/hmreu575.html) or if you're feeling more adventurous, there's a certain guy in Ohio selling them on eBay for a whopping $2.75 each + shipping (I bought 10 at that price...). I say adventurous, because the guy's clearly crazy. He's selling clothing, U-Joints, and paper envelopes full of "fresh, Ohio farm air." Sorry, but per forum rules, I can't post that link to the eBay listing.